The present invention relates to a crank angle detecting system for an internal combustion engine for vehicles. The detected crank angle is used for controlling the fuel injection timing and ignition timing of the engine.
Heretofore various methods for sensing the crank angle have been proposed and used. Japanese Patent Application Laid-Open No. 55-66620 discloses a system in which a crankshaft is provided with a pulley having V-shaped notches on the periphery thereof. The crank angle is determined by sensing the position of the notch. Further, as another method, a system for detecting the crank angle dependent on the position of a camshaft is used.
However, in case of a multi-cylinder engine, the former system can not discriminate the crank angle for each cylinder. As an example of the latter system, the crank angle is detected by a rotor plate having slits. The rotor plate is provided in a distributor or secured to the camshaft, and an optical sensing system comprising a light emitting diode and a photo diode is provided for sensing the position of the slits. Such a system entails high manufacturing cost. Furthermore, a timing belt for driving the camshaft may vibrate or deteriorate with time, and will extend or contract by thermal expansion during operation. Accordingly, it is difficult to detect the crank angle accurately.